RESTful URI should refer to a resource that is a thing (noun) instead of
referring to an action (verb) because nouns have properties as verbs do
not. The REST architectural principle uses HTTP verbs to interact with
resources.

Though, there is an exception to that rule, verbs can be used for
specific actions or calculations, .e.g.:

If you use singular for a collection like resource (e.g. “/user” to
retrieve a list of all users) it feels wrong. Mixing singular and plural
is confusing (e.g. user “/users” for retrieving users and “/user/21” to
retrieve a single user).

Versioning APIs does make a lot of sense for public API services.
Especially if an API provider needs to ship different versions of the API at the same time.
Though, Plone already has a way to version packages and it currently does not make sense for us to expose that information via the API.
We will always just ship one version of the API at a time and we are usually in full control over the backend and the frontend.